There is a _lot_ of info about Santana's around SF bay. Why not walk
around and ask around. You can find lots of examples and experiences.
Those sound like HUGE chain plates for that boat. Even if you postulate
that all the pitted metal is just cut out, the remaining stuff would
probably still be over kill. Since the plates are out, maybe you could
go walk into a surveyer's office and get his opinion on the spot.
However, by talking with local owners (or on the web), you can find out
what common practice is, and at least get new ones more or less sized to
that boat. The "hole in the roof" would need a little extra caulking,
though. Slotted cover plates that slide down the chain plate onto the
deck surface really make a difference to leaking.

If the bulkhead is messed up, get new metal double or triple the
original length and bolt it into something that remains solid lower down
there. I think you would want to install it so the upper shroud (the one
with the most load) gets the fair lead, but then again, ask around of
those who have done it before or take a look at a bunch of boats and see
what people have done.

Rufus